[Translated article] Biomechanical evaluation and analysis of a reused telescopic intramedullary femoral nail in a child with achondroplasia.

INTRODUCTION

Telescopic intramedullary nails (TIMN) have represented a significant advancement in limb lengthening procedures. However, their elongation capacity is limited to 5cm in the bones of patients with achondroplasia. Consequently, techniques involving TIMN reutilization have been developed. This reuse presents mechanical and safety challenges due to material fatigue and repetitive loading, which may compromise the structural integrity of the implant. This study evaluates the biomechanical performance and potential damage of a reused TIMN.

METHODS

An experimental analysis was conducted on a femoral TIMN removed after two 5-cm lengthenings in a patient with achondroplasia. The nail was measured and examined following non-destructive deconstruction, material analysis, 3D reverse engineering modeling, and finite element analysis to assess its performance under various loading conditions.

RESULTS

Mechanical and chemical damage compromising the integrity of the nail was identified. The aged Ti6Al4V alloy was validated for its resistance to complex loads. The 3D model showed that the gear mechanism effectively transformed rotational into translational motion. Finite element analysis revealed that the safety factor reached its critical threshold at 2.44̊ and 2.25̊, indicating the nail was near its mechanical limit. The rod and guide were identified as critical components.

CONCLUSIONS

TIMN reuse should be approached with caution due to potential material fatigue. This study provides a foundation for redesigning these implants to improve their ability to withstand prolonged loading cycles.